1. Field of the invention
The present invention relates to the structure of a processing tank of a photosensitive material processing apparatus, and more particularly to the structure of a processing tank in which a desilverization reaction is performed and to that of a rack used therein.
2. Description of the related art
In a conventional photosensitive material processing apparatus for carrying out automatic development of a color photosensitive material, the steps of color development, bleaching, fixing, and stabilizing have been performed in a color development process. In the step of color development, dyes are produced while free silver--which forms latent images in sensitized portions--is reduced. In the step of bleaching, the silver--which forms latent images at the color-developed portions--is oxidized to be returned to the form of silver salt. In the step of fixing, the silver salt is converted into a water soluble complex salt and is removed. In the step of stabilizing, color-generating components at non-sensitized portions are deactivated so as to complete the development process. Through this process, stable images are obtained.
Various techniques have been employed so as to reduce the amount of a processing solution required in the development process, in consideration of cost and liquid waste treatment. In order to suppress exhaustion of the processing solution, various kinds of promoting agents are added. Moreover, the processing solution is agitated and circulated so as to obtain stable processing performance with a small amount of a processing solution and to enhance or maintain the activities of the processing solution and photosensitive material.
An example of a processing tank of a conventional photosensitive material processing apparatus will be described with reference to FIG. 1. To the processing tank 61 is connected a subtank 62. A pump 63 feeds a processing solution from the subtank 62 to the bottom portion of the processing tank 61 so as to circulate the processing solution, whereby the processing solution is fed into the lower portion or bottom portion of the rack 64 placed in the processing tank 61.
In order to decrease the amount of a processing solution required for processing of a photosensitive material, the activities of the processing solution and photosensitive material are chemically enhanced and maintained through use of a suitable promoting agent, and reaction is physically accelerated through agitation.
In the conventional photosensitive material processing apparatus, since a processing solution within the processing tank is agitated by feeding the processing solution from a side wall of the processing tank, the processing solution cannot be agitated sufficiently. Therefore, desilverization tends to become insufficient in the step of bleaching, fixing, or the like. If there is insufficient reaction for returning the silver --which forms latent images--to the form of silver salt, or if there is insufficient reaction for dissolving and removing the silver salt, excess silver remains on the photosensitive material, resulting in an increase in contrast, which deteriorates the image quality at a highlight portion. Moreover, when silver is not removed completely from a photosensitive material, there is a possibility that the image quality deteriorates when a long period of time has elapsed after development.